Influence of vertebrate and invertebrate infochemicals on the population growth and epizoic tendency of Brachionus rubens (Ehrenberg) (Rotifera: Brachionidae)

Brachionus rubens is often epizoic on large cladocerans. While this behaviour confers advantages in the presence of invertebrate predators, it is detrimental in the presence of vertebrate predators. This study aimed to determine whether the epizoic tendency of B. rubens varies in the presence of infochemicals from vertebrates and invertebrates. For the invertebrate predators we used Asplanchna brightwellii (Rotifera) and Acanthocyclops robustus (Copepoda) and for the vertebrate predator, the zebra fish (Danio rerio). We studied the population dynamics, morphometry and egg ratio of B. rubens in the medium in which the predators were maintained for 24 h and this was compared to controls (water without infochemicals). Experiments were conducted using 50 ml of test medium containing the algal food Chlorella vulgaris at a density of 1X10⁶ cells ml⁻¹. We introduced 5 individuals of Daphnia pulex into each container to quantify the number of epizoic individuals of B. rubens. The results showed that B. rubens suffered considerable exploitative competition from Daphnia pulex. Growth rates however did not vary significantly due to the presence of vertebrate or invertebrate infochemicals. In the presence of Daphnia more than 68% of B. rubens population was epizoic. The data have been discussed with special emphasis on the protective value of epizoic behaviour against predation pressure in nature.